Aerodynamic surfaces are employed in a variety of applications, such as flaps and other control surfaces of an aircraft. In use, fluid flows over the aerodynamic surface so as to establish a flow field. In some instances, the flow field that passes proximate the aerodynamic surface may be controllably altered in order to modify the performance provided by the aerodynamic surface. For example, an aerodynamic surface may employ active flow control in order to inject fluid or momentum into the flow field passing proximate the aerodynamic surface. Some traditional forms of active flow control include steady blowing or suction of a fluid, pulsed blowing or suction of a fluid and synthetic jets. Active flow control has also been provided by fluidic oscillators that generate self-oscillating jets so as to provide spatial and temporal oscillation. As a result of the active flow control, the flow field is controllably altered which correspondingly modifies the resulting performance provided by the aerodynamic surface as well as the performance of the vehicle or other structure that embodies the aerodynamic surface. In this regard, the injection of fluid or momentum into a flow field may mitigate the partial or complete flow separation of the flow field from the aerodynamic surface, thereby facilitating performance improvements.
Active flow control on lifting surfaces has primarily focused on the mitigation of partial or complete flow separation over stalled flaps or wing sections in an instance in which the separating shear layers are dominated by a strong coupling to the instability of the wake that leads to the nominally time-periodic formation and shedding of large-scale vortices. Thus, the manipulation and control of separation on an aerodynamic surface have typically been based on the narrow-band receptivity of the separating, wake-dominated flow to external actuation at a frequency corresponding to the instability of the near wake. This actuation induces a Coanda-like deflection of the shed vortices toward the surface of the stalled airfoil. An alternative approach to reducing flow separation which is decoupled from the global flow (wake) instabilities is a modification of the apparent aerodynamic shape of the surface which alters the streamwise pressure gradient upstream of separation. In this approach, actuation is affected by forming a controlled interaction domain of trapped vorticity between a surface-mounted fluidic actuator and the cross flow over the aerodynamic surface. Under this approach control is achieved using actuation having frequencies that are at least an order-of-magnitude greater than the characteristic wake frequency and are therefore decoupled from global flow instabilities. Thus, flow control is advantageously affected not only when the baseline flow is separated, but also when significant portions of the flow are attached, such as during cruise conditions at low angles of attack. However active flow control provided by fluidic oscillators has varying levels of efficiency and effectiveness, with some fluidic oscillators having a relatively large footprint.
With respect to aircraft, some aircraft, such as some transport aircraft, employ high-lift systems that influence the design and performance of the aircraft. In this regard, performance characteristics, such as maximum take-off weight, required runway length and stall speeds, are impacted by the high-lift systems. Historically, high-lift systems have included complex, multi-element designs with intricate positioning mechanisms to improve performance and efficiency. Although high-lift systems have been simplified, high-lift systems may be further improved in terms of weight, number of parts, fabrication costs and/or cruise efficiency. Thus, active flow control has been considered as an option to improve high-lift performance. In this regard, active flow control may enable increased levels of performance, such as an increased coefficient of lift CL, with reduced complexity. However, the manner of implementing active flow control in an efficient and effective manner for high-lift systems has yet to be resolved.